Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease, particularly, stenosis. “Stenosis” refers to a narrowing or constriction of the diameter of a vessel. In a typical PTCA procedure, a catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery to treat stenosis at a lesion site. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inner wall of the artery to dilate the lumen. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient's vasculature.
Restenosis of the artery commonly develops over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. “Restenosis” is the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated with apparent success. Restenosis is thought to involve the body's natural healing process. Angioplasty or other vascular procedures often injure the vessel walls, including removing the vascular endothelium, disturbing the tunica intima, and causing the death of medial smooth muscle cells. Excessive neoinitimal tissue formation, characterized by smooth muscle cell migration and proliferation to the intima, follows the injury. Proliferation and migration of smooth muscle cells (SMC) from the media layer to the intima cause an excessive production of extra cellular matrices (ECM), which is believed to be one of the leading contributors to the development of restenosis. The extensive thickening of the tissues narrows the lumen of the blood vessel, constricting or blocking blood flow through the vessel.
To reduce the chance of the development of restenosis, treatment substances can be administered to the treatment site. For example, anticoagulant and antiplatelet agents are commonly used to inhibit the development of restenosis. In order to provide an efficacious concentration to the target site, systemic administration of such medication often produces adverse or toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery, thus, produces fewer side effects and achieves more effective results.
Techniques for the local delivery of a treatment substance into the tissue surrounding a vessel are disclosed in U.S. Pat. Nos. 6,944,490, 6,692,466 and 6,554,801 to Chow et al. In some applications, such techniques include a catheter with a needle cannula slidably disposed in a needle lumen and a balloon, which is coupled to the distal end of the catheter. When the balloon is inflated the needle lumen is brought into close engagement with the tissue and the needle cannula can be moved between a position inboard of the catheter distal surface and a position where the needle cannula is projected outboard of the catheter to deliver the treatment substance to the tissue.
Needles which are used in conjunction with percutaneous injection devices and open-chest surgical injection devices generally include beveled single-port needle tips. Some of the problems associated with these types of needle tips include backflow of the injectate to non-focal areas, damage to surrounding tissue due to high focal injection pressure and reduced treatment agent dispersion due to localized delivery from a single port. Some studies have shown that up to 90 percent of the injectate never reaches the target tissue area due to backflow. As a result, treatment using needles often requires multiple injections which can result in increased pain and risk to the patient in addition to increased tissue damage due to multiple puncture wounds.
The treatment of organs with injection devices, in particular dynamic organs, also presents unique challenges. For example, the heart will generally be contracting during a treatment which increases backflow during each muscle contraction and decreases treatment agent dispersion. Moreover, injection devices with a single needle can be inadequate to treat a large injury region on the heart.